The use of radiation to treat medical conditions comprises a known area of prior art endeavor. For example, radiation therapy comprises an important component of many treatment plans for reducing or eliminating unwanted tumors. Unfortunately, applied radiation does not inherently discriminate between unwanted areas and adjacent healthy tissues, organs, or the like that are desired or even critical to continued survival of the patient. As a result, radiation is ordinarily applied in a carefully administered manner to at least attempt to restrict the radiation to a given target volume.
Brachytherapy a form of radiotherapy where one or more radiation sources are placed inside or next to the patient's target volume. The radiation sources are typically precisely placed (often using applicators through which the radiation sources can be moved) and are usually removed after completing a predetermined period of exposure (often referred to as dwell time).
A brachytherapy treatment plan for a specific patient will typically specify such things as the number of radiation sources, their strength(s), their placement, and their dwell time. Such treatment plans are often optimized (in whole or in part) prior to use. (As used herein, “optimization” will be understood to refer to improving upon a candidate treatment plan without necessarily ensuring that the optimized result is, in fact, the singular best solution.) Many optimization approaches use an automated incremental methodology where various optimization results are calculated and tested in turn using one or more automatically-modified (i.e., “incremented”) treatment plan optimization parameters (such as, for example, dwell time).
Such radiation sources are often placed within the patient's target volume but such is not always the case. Sometimes a treatment plan can best serve the overall objectives of the therapy if one or more radiation sources are positioned outside the patient volume. Such is often the case, for example, with ring and tandem applicators, vaginal cylinders, and surface applicators. For a variety of reasons, however, optimization techniques can be less successful when considering radiation sources that are not limited to placement within the target volume.
Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. Certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. The terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.